The very first climbing holds were rocks glued to cement walls using auto body resin. Training on the holds was tough, the chunks of rock tend to be clunky and sharp, and the glue holding the rocks blew at about every third use of the hold.

The first commercial walls were built in France in the 1970s and gradually climbers gravitated toward making cast holds out of ceramic and fired clay. Early on though, the hip thing was to make either single-digit pockets or ridges the diameter of a bread knife.

Completing a route made up of these early holds could be pretty miserable.

In the 1980s, the climbing hold company Entreprise starting marketing prefabricated panels that could be fit together to create walls. Huge outdoor Entreprise walls, with their natural-looking features and cool insets, have played host to international climbing comps for three decades. But their walls limit options for adding holds, and climbers favored walls allowing for complete route changes using a growing variety of cast holds.